How does the epidermis grow, shed or rebuild?
The epidermis makes new cells in the base layer which push up, flattening cells above them, which eventually flake off in desquamation, to be replace by the newer cells below.
The epidermis forms columnar cells in the base layer, furthest away from the surface. These cells are young and healthy, formed from dividing keratinocyte stem cells.
As more cells are made, they push upwards, and all the cells move up. This also squashes the young cells into flatter, more cuboid shapes.
The process continues, more living keratinocytes being produced, pushing the ones above them up, squashing them eventually until they have very little depth and are almost like flakes. Once they get to this point, they are dead, and after a while flake off.
Desquamation is the process of shedding the top layer of skin cells, which comes from a Latin word for scraping off fish scales, desquamare. It balances out the creation of new skin cells in the basal (base) layer.
The whole process takes around 14 days, from the young keratinocyte to the dead corneocyte on the top layer of skin.